Fuel tanks in vehicles may be vented during refueling, wherein fuel is replenished in the fuel tank, in order to reduce pressure in the tank during refueling. For example, a canister vent valve may be opened to put the fuel tank in communication with the atmosphere in response to a refuel request, e.g., a vehicle operator input to initiate refueling or a refueling door opening. In some applications, a fuel tank isolation valve may be coupled to a fuel tank to control fuel tank venting. For example, a fuel tank isolation valve may be located in a conduit between a fuel tank and a fuel vapor canister in an evaporative emission control system and actuated during certain conditions to vent the fuel tank.
In some applications, e.g., in a hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV), a sealed fuel system with a normally closed fuel tank isolation valve may be used to reduce evaporative emissions. In such applications, the fuel tank isolation valve may be actuated and held open during a refuel event to reduce fuel tank pressure build up. For example, such pressure increases during refueling may lead to fuel pump nozzle shut-offs. The inventors herein have recognized that powering a fuel tank isolation valve for any length of time when not necessary consumes power that reduces fuel economy of PHEV and HEV vehicles. For example, powering the valve continuously during a refueling event when the vehicle operator is not adding fuel to the fuel tank or is adding fuel to the fuel tank slowly may unnecessarily consume power leading to fuel economy reduction.
In order to address these issues, in one example approach a method for a vehicle with an engine comprises, in response to a refuel request, actuating a fuel tank isolation valve to vent a fuel tank for refueling; and, in response to a pressure in the fuel tank below a threshold pressure after a predetermined time duration, discontinuing actuation of the fuel tank isolation valve to seal the fuel tank.
In this way, a fuel tank isolation valve may be closed after a calibratable time period if the tank pressure is low to save power since low fuel tank pressure may indicate that fuel is either not flowing into the tank or is flowing in at a low rate from a fuel pump nozzle. The fuel tank isolation valve may then be re-opened/energized if/when pressure is seen to increase (due either to fuel flow from a nozzle or due to evaporation of the fuel) and may stay open until a time out occurs or if the fuel door is closed indicating an end of refueling event. Such an approach may result in a reduction of power consumption in the vehicle and an increased fuel economy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.